From 77a4be89599c587f8b1ac6256ad7dc11a8ce28fa Mon Sep 17 00:00:00 2001
From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Fri, 22 Sep 2017 23:43:46 +0300
Subject: USB: devio: Don't corrupt user memory

commit fa1ed74eb1c233be6131ec92df21ab46499a15b6 upstream.

The user buffer has "uurb->buffer_length" bytes.  If the kernel has more
information than that, we should truncate it instead of writing past
the end of the user's buffer.  I added a WARN_ONCE() to help the user
debug the issue.

Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index c8075eb..860108c 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -1577,7 +1577,11 @@ static int proc_do_submiturb(struct usb_dev_state *ps, struct usbdevfs_urb *uurb
 			totlen += isopkt[u].length;
 		}
 		u *= sizeof(struct usb_iso_packet_descriptor);
-		uurb->buffer_length = totlen;
+		if (totlen <= uurb->buffer_length)
+			uurb->buffer_length = totlen;
+		else
+			WARN_ONCE(1, "uurb->buffer_length is too short %d vs %d",
+				  totlen, uurb->buffer_length);
 		break;
 
 	default:
-- 
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